Question

Suppose that the instruction format for a modified Little Man Computer requires two consecutive locations for each instruction. The high-order digits of the instruction are located in the first mail slot, followed by the low –order digits. The IR is large enough to hold the entire instruction and can be addressed as IR [high] and [IR] low to load it. You may assume that the op code part of the instruction uses IR [high] and that the address is found in IR [low]. Write the fetch-execute cycle for an ADD instruction on this machine.

Answer 1

Answer:

// Fetch-execute cycle for an ADD instruction

PC →MAR

MDR → IR [high]

PC + 1 → PC

PC →MAR

MDR → IR [low]

IR [low] → MAR

MDR + A → A

PC + 1 → PC

Explanation:

• MAR  is assigned PC and IR[high] value is assigned to   MDR.
• Increment value of PC by 1 .
• Again MAR  is assigned PC  and A is assigned MDR.
• At the end, increment value of PC by 1 .